The present invention relates generally to quantum devices, and more specifically, to a quantum communication link that is robust against photon loss.
The fundamental element of a quantum computer is the quantum bit which is known as the “qubit.” As opposed to a classical bit representing zero and one, a qubit is also able to represent a quantum superposition of the two states. The states can be formalized within the laws of quantum physics as a probability of being in the two states. Accordingly, the states can be manipulated and observed within the laws of quantum physics.
Quantum properties include quantum entanglement and quantum teleportation of information, which is linked to the property of quantum entanglement. Quantum entanglement can exist between any two quantum systems such as between two photons, two atomic/ionic systems, or between a photon and an atom/ion based quantum system. Quantum communications can sometimes be used in conjunction with compression techniques involving the usage of qubits. Qubits are units of quantum information that can be visualized by a state vector in a two-level quantum-mechanical system. Unlike a binary classical bit, a qubit can have the values of zero or one, or a superposition of both. A qubit may be measured in basis states (or vectors), and a conventional Dirac symbol is used to represent the quantum state values of zero and one, such as for example |0 and |1. For example, on a physical qubit this can be implemented by assigning the value “0” to a horizontal photon polarization and the value “1” to the vertical photon polarization. The “pure” qubit state is a linear superposition of those two states which can be represented as a combination of a|0+b|1. However, transmitting quantum information/state (via a flying qubit, i.e., transmitting qubit) across a lossy channel such as, an optical fiber link, can yield a very low efficiently due to loss, and consequently one cannot access the information of the received quantum information/qubit state.
In computing science, the controlled NOT gate (also C-NOT or CNOT) is a quantum gate that is an essential component in the construction of a quantum computer. The CNOT gate can be used to entangle and disentangle EPR states. Any quantum circuit can be simulated to an arbitrary degree of accuracy using a combination of CNOT gates and single qubit rotations. Moreover, the CNOT gate is the quantization of a classical gate.